A vaccine of pneumococcal capsular polysaccharide will be administered to 200 children, ages six to fifteen months, who have had recurrent episodes of acute otitis media. The children will be observed for at least two years to determine the effectiveness of the vaccine in the prevention of pneumococcal otitis media. The study will be performed in double blind fashion; one-half the children will receive an octavalent pneumococcal vaccine containing eight types most frequently implicated in otitis media; the other half will receive a pneumococcal vaccine containing six types infrequently found as causes of otitis media.